Circulation weather types associated with extreme flood events in Northwestern Mediterranean

The aim of this work was to identify the circulation weather types associated with flood events that occurred in Catalonia (Northeastern Spain) during the period 1900-2010. To achieve this objective, 261 extraordinary and catastrophic flood and flash flood events that were recorded during this period were characterized and classified based on impact data. A preliminary analysis of maximum precipitation and discharge was conducted in order to have some quantitative hydrometeorological indicators associated with these kinds of events. The objective classification developed by Jenkinson and Collison, which is based on differences in synoptic patterns according to surface pressure, was implemented. Once the weather regimes for each flood event had been established, a statistical and comparative analysis was performed that allowed us to determine which synoptic patterns were more frequently associated with the different flood types, their differences and their similarities. The results show that most synoptic situations were pure cyclonic structures, in both extraordinary and catastrophic events, although they were more frequent in the latter. Catastrophic floods generally had a synoptic origin enhanced by certain mesoscale factors, while extraordinary floods were usually associated with local flash floods that occurred primarily in summer and early autumn, highlighting the undetermined types that were not reflected at a synoptic scale. As the Mediterranean basin is a region where floods cause serious socio-economic impacts, this work will help improve prevention measures and provide information for policymakers, mainly for land-use planning and early warning systems.